Insulated conductor



United States Patent C INSULATED CONDUCTOR Warren H. Eckels, Kingston, N. Y., assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware Application `lune 1.3, 1955, Serial No. 515,185 2 Claims. (Cl. 174-117) This invention relates to insulated conductors and more particularly relates to an insulated multiple conductor.

Multiple conductors, that is, a plurality of insulated wires joined together by a web between the adjacent wires, are well known and widely used in the electrical art. Common lamp cord is a duplex wire which is usually insulated by an extruded coating of rubber or soft vinyl plastic. The two insulated conductors are joined together by a relatively thin web of the insulatory material so that they may be bifurcated for the attachment of a male plug or attachment to an electrical appliance.

One of the larger uses for wire of this type is in electrical blasting caps wherein a duplex insulated wire is furnished in desired lengths up to and even exceeding 250 feet. The longer lengths are generally wound on a spool with the initiator being placed in the core for storage and transportation. Shorter lengths are usually bundled and secured by a paper band.

lt has been found that where duplex or multiple core wire is employed, and particularly in blasting operations, that the tearing apart or bifurcation of the duplex lead often causes incipient cracks to form in the web section which, when the individual leads are further bent with the torn web at the outside of the bend, actually result in an exposure of the bare conductor. Obviously, such tearing' of insulation and exposure of a conductor is highly undesirable, particularly in blasting operations where adverse moisture conditions are often encountered. rThis cracking resulting from the bifurcation of duplex or other multiple conductors is more or less serious depending, of course, on the softness of the insulatory material and the actual use to which the wire is put. lf the insulatory material is soft and readily tearable the web joining the coating of individual conductors will tear more cleanly and less cracks will be experienced. In like manner in uses where the wire will not be bent sharply with the severed web on the outside of the bend, less difculty is likely to be encountered. However, where the wire is employed in such operations as blasting and particularly when the insulatory coating and web are formed from a necessarily tough, abrasion-resistant, plastic material, the formation of cracks is encountered more frequently and the problem is much more acute. It has been found that the problem is probably most acute when the wire is coated with ethyl cellulose or an ethyl cellulose composition, insulatory materials which are otherwise highly desirable from the standpoint of toughiness, abrasion-resistance, dielectric constant and low temperature ilexibility.

Now in accordance with the present invention a manner of joining multiple conductors together with plastic insulation has been discovered which markedly reduces the amount of cracks formed and for most practical purposes substantially eliminates them.

Generally described, the present invention is an insulated multiple conductor comprising a plurality of ilexirice ble metallic conductors in substantially parallel relationship, a dielectric coating of plastic material formed about each separate conductor and an integral web of the plastic material joining the adjacent coated conductors, the web being disposed diagonally to a line drawn through the cross-sectional centers of the conductors. It has been found that marked reduction of cracking even with ethyl cellulose insulation has been obtained when the web is inclined from 30-70" to a straight line drawn through the cross-sectional centers of the conductors. Best results have been obtained when the angle of about 45 is employed. Good results are also obtained with larger angles but it has been found that the maintenance of dies forming such a conguration is more diiicult with the larger angles due to increased extruder die threading ditliculties. Thus, the smaller angles and in particular an angle of about 45 is preferred.

Having generally described the invention, more specific description of the insulated conductor of the invention and an embodiment of a die by which the conductor of the invention may be produced are discussed in connection with the accompanying drawing. In the drawing, Fig. l is a cross-sectional view of a coated duplex wire in accordance with the invention while Fig. 2 is a cross- `sectional view of a die with which such insulated duplex wire may be produced. Figs. 3 and 4 illustrate a wire testing method.

in Fig. l, a cross-section of a duplex blasting cap lead wire is shown in which the wires 10 are made of copper and have a diameter of 0.032 inch. An ethyl cellulose coating 11 and the diagonal web 12 are formed about the wires by an extrusion operation. The diagonal web 12 joining the two coated conductors is inclined at an angle of 45 to the line passing through the cross-sectional centers of the wires 10. ln production of this particular wire, an insulation thickness of .010 inch is employed. For such a thickness a web thickness of about .004-.005 inch is preferred.

In Fig. 2, a die 2i) is shown. Two spring steel, chisel edged die inserts 21 are positioned in the die as shown. The bevelled edges 22 of the inserts are formed with an angle of 45 to the normal. The wire 10 is drawn through this die by a conventional wire guide assembly (not shown) which maintains the wires in the position shown. When such a die is employed in a conventional wire coating machine, the coated wire shown in Fig. 1 is formed.

Aln order to compare the tear resistance of the duplex wire web in accordance with the invention, a series of ten 4-inch lengths 30 of a given duplex wire sample were cut and the web of each length was separated for l inch at one end. Then, as shown in Figs. 3 and 4, the pieces were placed one at a time beside a /lG-inch diameter mandrel 31 and each wire of the duplex pair was bent outwardly over it in turn as shown in Fig. 4. The wire was perpendicularly situated with respect to the mandrel in such a way that the end of the crotch 32 formed by the web separation was immediately beside the mandrel 3l, the mandrel resting perpendicularly against the insulation diametrically opposite the crotch. The innermost wires were bent outwardly from the web axis in such a direction that the web side of the insulation was on the outside of the bend and thus in tension at 33 where cracks 34 may form. A similar test was made with wire which was identical to that of the invention except that the web was formed by employing a conventional duplex die having two opposed symmetrically pointed inserts. The test above described was repeated over a period of ve months on samples taken from actual production until a total of 400 points for possible failure were tested with each type of web. Moreover, the test procedure employed produced a much more rigid test than even blasting cap Wire can be expected to be put in actual use. It was found that of the 400 possible points of failure, cracks formed only 14.2% of the time in the Wire of the invention While with the prior art Web employed for comparison failures were obtained 49.5% of the time. These results show better than a threefold improvement being achieved with the Wire produced in accordance with the invention. rThe insulation employed in the tests was an ethyl cellulose composition consisting of 94% ethyl cellulose and 6% dihexyl adipate.

As previously indicated, multiple coated Wire insulated with ethyl cellulose is more subject to the formation of cracks during very severe bending after bifurcation. However, definite beneiit may obviously be obtained With any plastic coating material Whether more or less tough than ethyl cellulose. Thus, any plastic material having suitable dielectric properties, toughness, abrasion-resistance and nexibility may be employed in the production oi multiple core conductors in accordance with the invention. Such materials in addition to ethyl cellulose include cellulose acet te, polyvinyl chloride, polyvinyl acetate, mixtures of polyvinyl chloride with polyvinyl acetate, nylon, acrylonitrile and the like and their compositions. Any type of conductive metal may be employed for the conductors or Wire. {ov/ever, copper and iron and aluminum are probably the most desirable. Gbviously, only a flexible conductor or Wire Will be employed in this type of multiple conductor.

ln addition to freedom from cracking in bending after bifurcation it has been found that duplex and other mul tiple wire produced in accordance with the invention will itself to a smaller Width during spooling operations. Thus, not only v/ill a more uniform lay of the Wire be obtained on small spools during traversing but more wire can be Wound on a spool of a given size. This advantage is due to the diagonal web which acts like an accordion fold and allows the wires to move closer together when force is applied from the outer sides.

Since modication of the invention as disclosed will occur to those skilled in the art, it is intended that the scope of the invention be limited only by the appended claims.

What l claim and desire to protect by Letters ?atent is:

l. in insulated multiple conductor comprising a pair of adjacent exible conductors in substantially partllel relationship each insulated 'oy a dielectric coating of an ethyl cellulose plastic material and an integral web of the said dielectric material joining7 the adjacent insulated conductors, and wherein the said material is char "cterizcd by the formation of incipient cracks in said web and the extension thereof into the insulation around a Wire when the web is torn and the said Wire is bent in the plane of the Wires over a cylindrical member with the torn web at the outside of the bend, the improvement comprising said web disposed to intersect at an angle of 30-70 with a line connecting the cross-sectional centers of the said conductors, and the ratio of thickness of the web to the thickness of the coating being in the range of from 0.4:1 to 0.511.

2. An insulated multiple conductor of claim l wherein the said Web intersects the said line of centers at au angle of about 45, the thickness of said plastic material being about 0.010 inch and the thickness oi the said web being in the range of about 0004-0005 inch.

ileterences (Cited in the file of this patent FOREGN PATENTS 477,019 Great Britain Mar. ll, 1936 

1. IN AN INSULATED MULTIPLE CONDUCTOR COMPRISING A PAIR OF ADJACENT FLEXIBLE CONDUCTORS IN SUBSTANTIALLY PARALLEL RELATIONSHIP EACH INSULATED BY A DIELECTRIC COATING OF AN ETHYL CELLULOSE PLASTIC MATERIAL ANN AN INTEGRAL WEB OF THE SAID DIELECTRIC MATERIAL JOINING THE ADJACENT INSULATED CONDUCTORS, AND WHEREIN THE SAID MATERIAL IS CHARACTERIZED BY THE FORMATION OF INCIPIENT CRACKS IN SAID WEB AND THE EXTENSION THEREOF INTO THE INSULATION AROUND A WIRE WHEN THE WEB IS TORN AND THE SAID WIRE IS BENT IN THE PLANE OF THE WIRES OVER A CYLINDRICAL MEMBER WITH THE TORN WEB AT THE OUTSIDE OF THE BEND, THE IMPROVEMENT COMPRISING SAID WEB DISPOSED TO INTERSECT AT AN ANGLE OF 30-70* WITH A LINE CONNECTING THE CROSS-SECTIONAL CENTERS OF THE WEB CONDUCTORS, AND THE RATIO OF THICKNESS OF THE WEB TO THE THICKNESS OF THE COATING BEING IN THE RANGE OF FROM 0.4:1 TO 0.5:1. 